Typically, gas operated firearms of the AR-15, AR-10 or M-16 platforms or the like include a receiver, a barrel, a bolt carried by a bolt carrier in the receiver and a “gas block” mounted on the barrel. The barrel is ported to the gas block and in one form of gas operated firearm, a gas tube extends rearwardly from the gas block toward the receiver and the bolt carrier. Gas pressure exits from the tube for operating the firearm through the transmission of a gas impulse, from the combustion of the cartridge, to the bolt carrier to cycle it and the bolt. In another form of a gas operated firearm, known as the “piston” gun, gas pressure ported from the barrel drives a rearwardly extending piston which engages the bolt carrier to cycle the firearm. In these firearm platforms the barrel is secured to the receiver by a barrel nut engaging a barrel flange and threaded to the receiver. In typical production, after the gas block is installed on the secured barrel, then a muzzle brake, flash hider or other barrel end device is typically mounted onto the muzzle end of the barrel. The outer parameters of these items do not permit installation of the barrel nut after these items are installed.
This system inherently presents several disadvantages adversely affecting the firearm, its reliability, its repair, and its assembly process.
Significantly it will be appreciated that any misalignment of the gas block on the barrel, for any reason, as in original assembly or in later repair or rugged field use can cause the weapon to fail.
As in one example, in assembling the firearm, the barrel is first fitted to the receiver and secured thereon by the threaded barrel nut which is passed over the barrel. The gas tube, gas block, any front sight and any barrel end device is then assembled with the front end of the gas tube being pinned into the gas block. Typically the gas block is pinned in position on the barrel. The structure and outside dimensions of the gas block in particular requires the barrel nut to be applied over the barrel before the gas block or the other components, such as any muzzle end device like a flash hider or muzzle brake, are fitted to the barrel. The internal diameter of the barrel nut is insufficient to allow the nut to be passed over the barrel and over the typically bulky gas block or muzzle end devices.
Alignment of the gas port of the barrel with the gas-receiving port of the gas block is thus problematical and must be done after the barrel nut is passed to the rear end of the barrel to secure it to the threaded receiver. This typically requires assembly fixtures for the receiver and/or barrel. Also any sight fixture and any muzzle end device must be fitted to the barrel after the barrel nut passage and for the same reason, particularly if the outside dimensions of the device exceeds the internal dimension of the barrel nut. The gas or gas tube or gas block, positioning pin is typically driven into the gas block, tending to torque the barrel, requiring compensation of that force.
Thus the typical requirement of fitting the barrel nut over the barrel before assembly of the gas block and gas tube and any muzzle end device leads to necessary assembly procedures.
This structure and associated assembly process inherently conflicts with related processes including, for example, any attempted field replacement of a defective or damaged gas tube. If a gas tube leaks or is damaged so as to interfere with firearm function, it must be replaced. In the past, this requires the gas block pin engaging the gas tube, and/or the block positioning pin, to be driven out of the gas block. Such pin removal forces torque or tend to turn the barrel, the gas block and the receiver of the firearm. This typically requires one or more fixtures holding the barrel, gas block, and/or receiver, as well as a barrel nut wrench to hold the nut. And once the positioning pin and gas tube is removed, if the barrel nut is loosened, a wrench must be used to re-torque and align the nut with a new tube. Again, the barrel must be held while the gas tube is oriented so that its parts align with the barrel parts and while the new tube is positioned and held in the gas block by driving a new pin therein.
These mechanizations render the replacement of a gas tube more complicated than is field expedient.
In addition to the original assembly process of aligning the gas block ports with the barrel ports, after the barrel nut passage, it is only after application of the barrel nut down the barrel that muzzle-end devices, having outside dimensions exceeding the internal dimensions of the nut, can be affixed to the barrel.
Also, it will be appreciated that the prior assembly process limits the outside diameter of the barrel forward of the gas block to dimensions not exceeding those of the interior of the gas block, which must be slid over the barrel after the barrel nut is applied.
It is thus apparent that the limited internal diameter of the barrel nut forces a particular assembly sequence, severely limiting the gas block, tube, muzzle device and other structural components and assembly techniques, as well as field expedient gas tube replacement.
Accordingly, it is an objective of this invention to provide an improved gas system and barrel structure for a gas operated firearm of either the direct gas impingement type of the gas driven piston type and without the prior limitations demanded by the barrel nut and the barrel components as noted.
It is a further objective of the invention to eliminate alignment problems between the gas block and barrel of a gas-operated firearm.
It is a further objective of the invention to provide a gas operated weapon wherein an integral barrel, gas block and optional muzzle device can be assembled to the receiver prior to the assembly of barrel nut thereto.
It is a further objective of the invention to provide field expedient processes and structure for gas tube replacement in a gas-oriented firearm.
It is yet a further objective of the invention to provide improved apparatus, structure and related methods for a gas operated firearm.